Patent GB-356741-A (GB)
Title: Improvements in or relating to the concentration of solutions of lower aliphatic acids
IPC: C07C51/46
Filed: 1930-05-30
Abstract: Acetic, propionic, butyric, and other lower aliphatic acids are concentrated by treating the aqueous solution or the vapour thereof with the vapour of an entraining liquid which may be a hydrocarbon such as benzene or xylene, a halogenated hydrocarbon such as trichlorethylene, dichlorethylene, or ethylene dichloride or an ester such as ethyl, propyl or butyl acetate; or a mixture such as ethyl acetate and benzene.  The heated aqueous acid may be treated with the entraining vapour until the water is removed; for instance, the solution may be introduced into a fractionating column in counter-current to the entraining vapour, the concentrated acid being subsequently freed from entraining agent by distillation. Alternatively, when the entraining agent is of lower boiling point than the acid, the entraining vapour may be introduced above the bottom of the column, the bottom of the column being heated, for instance to the boiling point of the entraining agent, so that the concentrated acid is obtained free from entraining agent.  Preferably both the dilute acid and the entraining agent are introduced in vapour form into a fractionating column, which may be mounted on a still containing boiling concentrated acid; dilute acid vapour and entraining vapour being introduced about one-third of the way from the lower end of the column; the condensate may be allowed to separate into layers, the entraining agent being returned to the system.  A dephlegmator may be used above the column, and the heat of the vapours escaping from the top and the heat of the concentrated acid may be utilized, for instance for preheating the dilute acid or entraining agent.ALSO:Acetic, propionic, butyric, and other lower aliphatic acids are concentrated by treating the aqueous solution or the vapour thereof with the vapour of an entraining liquid which may be a hydrocarbon such as benzene or xylene, a halogenated hydrocarbon such as trichlorethylene, dichlorethylene or ethylene dichloride, or an ester such as ethyl, propyl or butyl acetate; or a mixture such as ethyl acetate and benzene.  The heated aqueous acid may be treated with the entraining vapour until the water is removed; for instance the solution may be introduced into a fractionating column in counter-current to the entraining vapour, the concentrated acid being subsequently freed from entraining agent by distillation. Alternatively, where the entraining agent is of lower boiling-point than the acid, the entraining vapour may be introduced above the bottom of the column, the bottom of the column being heated, for instance to the boiling-point of the entraining agent, so that the concentrated acid is obtained free from entraining agent.  Preferably both the dilute acid and the entraining agent are introduced in vapour form into a fractionating column, which may be mounted on a still containing the boiling concentrated acid; dilute acid vapour and entraining vapour being introduced about one-third of the way from the lower end of the column ; the condensate may be allowed to separate into layers, the entraining agent being returned to the system.  A dephlegmator may be used above the column and the heat of the vapours escaping from the top and/or the heat of the concentrated acid may be utilized for instance for preheating the dilute acid or entraining agent.